This invention relates to the production of hydrocarbons from an unconsolidated hydrocarbon-bearing formation that is penetrated by a well that communicates with the unconsolidated formation.
Hydrocarbons are sometimes found in subterranean unconsolidated formations. Such formations are normally poorly cemented sandstone formations which may in some instances have little or no cementing material holding the sand grains together.
The production of hydrocarbons from unconsolidated formations may result in the production of sand from the formation along with the hydrocarbons. The production of sand is undesirable for many reasons. It is abrasive to components within the well such as tubing, pumps, and valves, and may partially or completely clog the well. Sand production is normally rate-sensitive, that is, no sand may be produced at very low rates while at high rates large quantities of sand may be produced.
Various techniques have been used for controlling the flow of sand from unconsolidated formations. Many of these techniques employ the use of slotted or screened liners or gravel packs to prevent the sand from being transported along with the hydrocarbons into the well. Other techniques make use of consolidating plastic material to cement the grains together and thereby prevent caving.
In U.S. Pat. No. 2,998,065 there is described an invention which relates to a method and apparatus for the completion of wells in unconsolidated sand formations whereby the sand particles in an unconsolidated-producing formation are supported under pressure from within the wellbore in order to prevent their entrainment in fluids flowing from the formation into the well. It is there stated that unconsolidated sand formations can effectively be controlled by the application of force to the walls of the borehole within the formation, thus creating pressures which counteract the pressures tending to break down the formation and cause entrainment of sand particles in he producing fluids. The pressures should be substantially equal to but not in excess of the overburden pressure. A porous-producing medium is positioned in the borehole and expanded to force the medium against the formation so that the sand particles are retained in their original, undisturbed position, to virtually eliminate sand production and the difficulties associated therewith. The porous-producing medium may comprise an expansible perforated sleeve or liner, a bed of gravel, or similar granular material, a tapered production liner, or a bed of metallic burrs or the like which can be forced into the formation and interlocked. In another embodiment, a gravel pack is used as the producing medium and a tubular sleeve is expanded against the gravel pack to create the necessary pressure. Another embodiment is described as being particularly adapted for use in boreholes wherein considerable washout has occured during drilling and wherein the diameter of the borehole within the unconsolidated formation is too large or irregular to permit use of the apparatus described. A perforated production tube sealed at the bottom is lowered into the well and a gravel pack is placed around the production tube by circulating a gravel-laden drilling mud through the annulus of a borehole and withdrawing the liquid free of gravel through the tubing to the surface. Water is then circulated through the borehole to wash any remaining drilling mud from the formation and the gravel pack. A piston is created above the gravel pack by introducing successively finer grades of solid material until an impervious layer several feet thick has been build up, thereby forming a piston. Liquid is introduced into the annulus of the borehole and the weight of the liquid on the piston compresses the gravel pack and forces it outward against the formation, creating the necessary pressure.
In U.S. Pat. No. 3,194,312 there is described an invention which relates to a method and apparatus for the completion and production of oil wells. Formation protecting and production valve units are connected in a conventional string of well casing and are positioned adjacent a producing formation. An expansible jacket is expanded outwardly into fluid-tight protecting and sealing engagment with the surrounding producing formation. While the jacket remains expanded, cement is forced downwardly through the casing string and flows upwardly exteriorly of the casing to cement the casing string within the wellbore. The cement cannot pass between the inflated jacket and the wellbore and thus the producing formation remains permanently free of the cement. Tube ports are provided in the formation protecting and production valve units such that the producing formation is placed in direct communication with the interior of the casing string, allowing the oil to flow from the formation into the casing.
In U.S. Pat. No. 3,756,318 to Nathan Stein and Lloyd G. Jones there is described a well completion system and a process for producing fluids from wells that penetrate unconsolidated formations. A sand retainer is installed adjacent a lower portion of an open production interval to control the production of sand from the zone of the unconsolidated formation that is subject to being invaded by a water cone. Fluids are produced from the well at a rate such that sand arches are formed and the formation is stabilized, thus permitting a high rate of production of hydrocarbons with a minimum production of sand from that portion of the unconsolidated formation above the sand retainer.
The formation of sand arches and the resulting stabilization of unconsolidated formations are discussed in an article entitled "Stability of Sand Arches: A Key to Sand Control", By C. D. Hall, Jr. and W. H. Harrisberger, Journal of Petroleum Technology, July 1970, pp. 821-829, and the aforementioned Stein and Jones patent. Stein and Jones teach that sand arches are formed as the result of cohesion or capillary forces between the sand grains and state that the formation is stabilized as the result of the overburden stress acting on the sand grains in the arch. They indicate that sand arches are the mechanism by which water-wet unconsolidated formations are consolidated, thus allowing hydrocarbon fluids to be produced at high rates therefrom without producing any substantial amount of sand from the formation. In describing an aspect of their invention wherein there has been no substantial disturbance of the unconsolidated formation by the production of fluids therefrom, Stein and Jones teach that it is preferable that the sand arches are formed slowly around each perforation to stabilize the formation. This is done by incrementally increasing the production rate and producing at each rate until sand-free production is obtained. This incremental increase in the production rate is continued until either the flow capacity of the production tubing is reached or until formation stability is no longer attained (sand-free production not attainable). By forming the sand arches in accordance with this procedure, sudden shifts within the formation are avoided thereby lessening the chance of the occurrence of formation failures. In addition, the chance is lessened for a large volume of sand to be produced when the well is first put on production.